Neural stem/progenitor cell study offers novel avenues for understanding the etiology and for developing potential treatment of many developmental and behavioral brain disorders and brain cancers. At the center of the study is how a delicate balance between the two key states of stem/progenitor cells, the self-renewal state and differentiation state, are maintained by intrinsic and extrinsic mechanisms in development and in adult life, because a defect in this homeostasis of neural stem/progenitor cells causes malformation of the brain and may even lead to tumor formation. Research over the past decade has thus far uncovered dozens of genes that are important for this regulation by either promoting self-renewal or stimulating differentiation, however, this progress represents only the beginning of our understanding on this fundamental stem cell biology issue. In this application, we propose to systematically and comprehensively characterize genes that are specifically expressed in neural progenitor cells and use this information to further identify causal factors crucial for the control of neural progenitor homeostasis. Our rationale is that by knowing the relevant factors involved in this process, we will be in a better position to elucidate the mechanisms that help specify the self-renewal and differentiation state of neural progenitor cells. To this end, we have developed a novel genetic two reporter system that enables isolation of endogenous neural progenitor cells and their direct progeny from the developing mouse brains. The purified neural progenitor cells and progeny will allow us to perform comparative gene expression analyses to identify differentially expressed genes. By identifying and characterizing these differentially expressed genes, we expect to uncover key regulators of neural progenitor homeostasis. This will ultimately help understand what and how equilibrium of molecular interactions in neural progenitor cells guides the balance between self-renewal and differentiation and how dysregulation in individual molecular axis may lead to a particular pathological condition in brain disorders.